Enrichment of oxygen for the production of hydrogen from hydrocarbons with co2 capture

ABSTRACT

The invention relates to a device which is used to produce hydrogen from a hydrocarbon, obtaining high energy efficiency and generating low levels of carbon dioxide and pollutants. The inventive device comprises (a) a conversion reactor which is used to convert the aforementioned hydrocarbons using water vapour. According to the invention, pure or almost pure oxygen is fed into the reactor in order to oxidize one part of the hydrocarbons and to provide the heat necessary to convert virtually all of the other part of the hydrocarbons into hydrogen, carbon monoxide and carbon dioxide. The device also comprises: (b) means of pre-heating the hydrocarbons, the oxygen flow and the water to be vaporized; (c) at least one heat exchanger which is used to cool the conversion product in order to recovery a fraction of the thermal energy of said conversion product; and (d) hydrogen-enrichment equipment. The above-mentioned reactor, the pre-heating means, the heat exchanger and the enrichment equipment all operate at high pressures, e.g., above 30 bars.

The present invention concerns a method and a device for producinghydrogen from a hydrocarbon with high energy efficiency while releasinglow or zero levels of carbon dioxide and pollutants.

In the sense of the present invention, the term hydrocarbon generallydesignates any fossil or renewable fuel, including substances that areoxygenated (alcohol, ester, etc.), gaseous, liquid, or even in powderedsolid form (handleable like a fluid), provided that it forms only asmall amount of inert solid residue, i.e., an ash content of less than1% by weight.

In essence, hydrogen as such does not exist in a natural state and mustbe produced, for example for use in fuel cells, either in a centralizedway in order to be distributed to local retailers and users, or in adecentralized way, locally, just upstream from the fuel cell, forimmediate consumption by the latter.

Hydrogen can be produced from two separate sources: either by so-called“downstream” means, i.e. by breaking down water thermally at a very hightemperature or electrically by electrolysis, or by so-called “upstream”means, by converting a hydrocarbon.

Since the hydrogen is intended to subsequently produce electricity in afuel cell, the use of “electrolysis” may seem inappropriate, at least interms of overall energy efficiency. But if this electricity is from arenewable (wind, solar, geothermal) or nuclear source, there is noproduction of CO₂ or other pollutants in this production-consumptionchain. Whether for stationary or mobile applications, the hydrogen inthat case seems to be an energy vector, making it possible, through theuse of fuel cells, to produce clean electricity in places that aretotally or periodically without access to nuclear or renewable energy.

In the “upstream” method, the conversion of a fossil or renewablehydrocarbon generates hydrogen but also CO₂, which may limit theadvantage of using fuel cells. However, this method has the advantage ofpotentially high energy efficiency, thus conserving fossil fuelresources or biomass products for energy uses.

There is therefore an emerging need for technologies for the centralized(large-scale) or decentralized (small-scale) production of hydrogen withhigh energy efficiency and low generation of CO₂ or other pollutants.

There are three main families of known methods for producing ahydrogen-rich mixture. These three methods are described theoreticallybelow:

1. First family: Partial Oxidation combined with Water-Gas ShiftConversion (POX+WGS).

The partial oxygen (POX) reaction corresponds to the reaction of thefuel (C_(n)H_(m)O_(p)) with oxygen. It results in the formation ofgaseous mixture of hydrogen, carbon monoxide, and possibly nitrogen (ifthe oxygen is drawn from the air):C_(n)H_(m)O_(p)+[(n−p)/2] (O₂+λN₂)→nCO+(m/2)H₂+[(n−p)/2]λN₂

λ represents the N₂/O₂ molar ratio of the oxidant mixture (standard airor oxygen-enriched air: λ<3.762). The POX reaction is exothermic; itdoes not require an external supply of heat. Having extracted thehydrogen from the fuel, it is possible to produce more of it using theso-called water-gas shift or WGS reaction, in which the carbon monoxidereacts with the water vapor to form carbon dioxide and additionalhydrogen through the following reaction:CO+H₂O→CO₂+H₂

Finally, the combination of the POX and WGS reactions is written asfollows:C_(n)H_(m)O_(p)+[(n−p)/2](O₂+λN₂)+nH₂O→nCO₂+(n+m/2) H₂+[(n−p)/2]λN₂

POX, being endothermic, produces less hydrogen than the vapor reforming(second family of methods) described below, and moreover, has a tendencyto produce solid carbon, which can foul or clog the tubes andexchangers. For example, in the case of gasoline, it is performed ataround 1200° C. without a catalyst and at around 800° C. with acatalyst. For diesel fuel, it is conducted between 950° C. and 1200° C.(Texaco-Shell™ burners).

2. Second family: Complete Vapor Reforming (VRC)

It is also possible to produce hydrogen from the fuel using the vaporreforming (VR) reaction, the principle of which is to oxidize the carbonin the fuel by reducing the number of water molecules in the gaseousphase.C_(n)H_(m)O_(p)+(n−p)H₂O→nCO+(n+m)/2−p)H₂

This reaction, automatically performed on a catalyst, is very highlyendothermic: this means that it requires an external supply of heat,which makes the generating system complex. This supply may be producedeither through external combustion of a fraction of fuel, or byrecovering excess heat. The concatenation of the VR and WGS reactions isknown as Complete Vapor Reforming (VRC) of the fuel, and is written asfollows:C_(n)H_(m)O_(p)+(2n−p)H₂O→nCO₂+(2n+m)/2−p)H₂

Vapor reforming is a reaction that is well known in petrochemistry,where the production of hydrogen from natural gas is common. It requiresa nickel-based catalyst, adapted to the molecules to be reformed(methane and light hydrocarbons). It is done at a temperature of 850 to950° C. at pressures of 15 to 25 bar and at H₂O/F (fuel) ratios between2 and 4. These reactions, being endothermic, are conducted in largefurnaces or banks of parallel tubes filled with catalysts and heatedexternally (mainly by radiation), which are passed through by themixture to be reformed. The energy required for the reforming reactionis produced by oxidizing part of the fuel with air (producing CO₂ andH₂O) and is transmitted to the reagents to be reformed through the wallsof these tubes.

For other hydrocarbons, the conditions and catalysts are different. Forhydrocarbons that are heavier than methane, the temperatures are lowerthan for methane (850° C.). Methanol is easier to reform; temperaturesof 250° C. are sufficient, and the catalyst is Cu/Zn/Al-based. Reforminggasoline requires a temperature higher than 800° C. Hydrocarbons thatcontain sulfur require pre-desulphurization, as the catalyst would bepoisoned by the sulfur. The reforming is therefore done undertemperature and pressure conditions that are adapted to the fuel andthat can be calculated using the laws of thermodynamics involvingchemical equilibrium. It is always a slow reaction, which is why thereforming is necessarily catalytic.

3. Third family: Autothermal Vapor Reforming (VRA)

In this method, a fraction of the fuel, which we'll call v, is burned inthe reformer in order to supply exactly enough energy to produce theendothermic complete vapor reforming reaction of the remaining fraction(1−v) of the fuel. The Autothermal Vapor Reforming reaction is thustheoretically a thermal. It is usually produced catalytically, attemperature levels between that of the POX-based method and that of theVRC method, for example on nickel at 25 bar and at 950° C. It is writtenin the following way:C_(n)H_(m)O_(p)+v(n+m/4−p/2)(O₂+λN₂)+[(1−v)(2n−p)−v(m/2)]H₂O→nCO₂+(1−v)(2n+m/2−p)H ₂+vλ(n+m/4−p/2)N₂

The fraction v that should be burned depends solely on the atomiccomposition of the fuel and its heat-generating power, as well as thatof the hydrogen. VRA is a combination of reforming and partial oxidation(with water and air injection). This technology has been adapted forsmall-scale facilities both in EPYX™ technology and in single-reactorHOTSPOT™ technology, initially developed for methanol.

In all reforming techniques, there is an energy need that is satisfiedby oxidizing part of the fuel with atmospheric air. This oxidation takesplace outside the hydrogen producing reactor in the case of vaporreforming, or inside the hydrogen producing reactor in the case ofpartial oxidation and autothermal vapor reforming. It consumes oxygenand produces CO₂.

The air is compressed before being introduced into the reformingprocess. In the case of a reforming process in connection with a fuelcell, air is also compressed in order to be introduced into the fuelcell. The air compressors represent auxiliary equipment that consumes asignificant part of the electric power produced by the fuel cell. Tolimit this consumption, the tendency is to use low levels ofpressurization relative to the atmospheric pressure, both for the fuelcell and for the reforming process when it is performed in directconnection with a fuel cell.

The invention concerns a method for producing hydrogen from ahydrocarbon with high energy efficiency while releasing very low or zerolevels of carbon dioxide and pollutants.

The method comprises a step (a) for using a flow of (pure or nearlypure) oxygen to (i) oxidize a portion of the hydrocarbons and (ii)supply the heat required to convert, using water vapor, at suitabletemperatures, nearly all of the other portion of the hydrocarbons intohydrogen, carbon monoxide and carbon dioxide. Suitable temperaturesmeans temperatures like those used in the techniques described above.

The method also comprises a step (b) for preheating the hydrocarbons,the flow of oxygen and the water to be vaporized. The hydrocarbons, theflow of oxygen, and the water to be vaporized are hereinafter referredto as the reagents.

The result of this combination of technical characteristics is that,nitrogen being absent from the reagents, there is no generation ofnitrous oxide and no need for energy to preheat it. The hydrogenproduction yield is thus distinctly improved.

The mixture formed by the hydrogen, the carbon monoxide, the carbondioxide and the excess water vapor is hereinafter referred to as theproducts of the conversion. Nitrogen being absent from the reagents, itdoes not dilute the conversion products; the subsequent steps (b)through (f) of the method are facilitated, and overall efficiency isincreased.

The method also comprises steps (c) for cooling (at least one) of theconversion products in order to recover a fraction of the thermal energyof the conversion products for the purpose of preheating the reagentsand condensing at least part of the water vapor contained in theconversion products.

The method also comprises the following steps:

a step (d) for recovering the hydrogen by extracting the hydrogen fromthe conversion products, either in order to consume it or with a view tostoring it for later consumption.

Steps (a) through (d) are performed at suitably high pressures, above 30bar, in order to:

-   -   intensify the heat exchanges, and/or    -   increase the compactness of the method, and/or    -   promote the liquefaction of the carbon dioxide by cooling,        and/or    -   promote the condensation of the water vapor by cooling, and/or    -   improve the overall efficiency.

Preferably, the method according to the invention also comprises:

steps (e) for the final conversion of the carbon monoxide into carbondioxide; if necessary, these steps are performed during the step forrecovering the hydrogen.

The result of this combination of technical characteristics is that, atthe end of steps (a) through (e), the residual flow no longer contains,apart from the water vapor that has not yet condensed, anything otherthan carbon dioxide.

Preferably, the method according to the invention is performed atsufficient pressure to implement:

a step for condensing (f) the carbon dioxide contained in the conversionproducts and/or the final conversion products,

a step for capturing the carbon dioxide in liquid form.

Preferably, the method according to the invention uses a membrane thatis selectively permeable to hydrogen to extract the hydrogen from theconversion products. In the case of this variant of embodiment, themethod also comprises a step for lowering the partial pressure of thehydrogen downstream from the membrane by diluting the flow of permeatedhydrogen in a flow of extraction gas, particularly a condensable gas.The result of this combination of technical characteristics is that thepermeation of the hydrogen is facilitated.

Preferably, in the case of this variant of embodiment of the invention,the extraction of hydrogen by means of a permeable membrane is performedat the same time as the step for the final conversion of the carbonmonoxide into carbon dioxide. The result of this combination oftechnical characteristics is that the partial pressure of the hydrogenduring the final conversion step is lowered, which promotes theconversion of the carbon monoxide into carbon dioxide.

Preferably, in the case of this variant of embodiment of the invention,the method also comprises a step for regulating the temperature of thefinal conversion by adjusting the flow rate and/or the temperature ofthe flow of extraction gas.

Preferably, according to the invention, the method is such that thepreheating and cooling steps are combined in a recovery exchanger sothat the reagents and the conversion products circulate continuouslythrough the recovery exchanger.

Preferably, in the case where the method is more specifically intendedto produce hydrogen for the purpose of feeding a fuel cell running withair, the method according to the invention also comprises a step forlowering the pressure of the conversion products and/or the finalconversion products and/or the hydrogen produced while compressing theair required to run the fuel cell.

Preferably, the method according to the invention can also be combinedwith a hydrogen production method that generates a flow of oxygen,particularly by electrolysis. The result of this combination oftechnical characteristics is that it is thus possible:

to limit the cost of producing the oxygen consumed in the methodaccording to the invention, and

to increase the overall quantity of hydrogen produced.

Preferably, the method according to the invention can also be combinedwith a nitrogen production method that generates a flow of oxygen. Theresult of this combination of technical characteristics is that it thuspossible to limit the cost of producing the oxygen consumed in themethod according to the invention.

The invention concerns a device for producing hydrogen from ahydrocarbon with high energy efficiency while releasing very low or zerolevels of carbon dioxide and pollutants. The device comprises a reactorfor converting (a) the hydrocarbons using water vapor. The conversionreactor is supplied with pure or nearly pure oxygen in order to (i)oxidize a portion of the hydrocarbons and (ii) supply the heat requiredto convert into hydrogen, carbon monoxide and carbon dioxide, atsuitable temperatures, nearly all of the other portion of thehydrocarbons. The mixture formed by the hydrogen, the carbon monoxide,the carbon dioxide and the excess water vapor is hereinafter referred toas the products of the conversion.

The device also comprises means for preheating (b) the hydrocarbons, theflow of oxygen and the water to be vaporized. The hydrocarbons, the flowof oxygen and the water to be vaporized are hereinafter referred to asthe reagents.

The device also comprises:

at least one heat exchanger (c) for (i) cooling the conversion products,for (ii) recovering a fraction of the thermal energy from the conversionproducts in order to preheat the reagents, and for (iii) condensing atleast a part of the water vapor contained in the conversion products.

a hydrogen recovery unit (d).

The hydrogen recovery unit comprises an extraction element forextracting the hydrogen from the conversion products in order to consumeit in a hydrogen-consuming device (for example in a fuel cell) or storeit in a reservoir for later consumption.

The conversion reactor, the preheating means, the heat exchanger, andthe recovery unit operate at suitably high pressures, above 30 bar, inorder to:

-   -   intensify the heat exchanges, and/or    -   increase the compactness of the method, and/or    -   promote the liquefaction of the carbon dioxide by cooling,        and/or    -   promote the condensation of the water vapor by cooling, and/or    -   improve the overall efficiency.

Preferably, the device according to the invention also comprises:

at least one reactor for the final conversion (e) of the carbon monoxideinto carbon dioxide, if necessary combined with the hydrogen recoveryunit.

The result of this combination of technical characteristics is that theresidual flow that leaves the device according to the invention nolonger contains, apart from the water vapor not yet condensed, anythingother than carbon dioxide.

Preferably, according to the invention, the pressure inside the deviceis sufficient to implement:

a condenser (f) for condensing the carbon dioxide contained in theconversion products and/or the final conversion products,

a container for storing the carbon dioxide in liquid form.

Preferably, according to the invention, the extraction element includesa membrane that is selectively permeable to hydrogen for extracting thehydrogen from the conversion products. The extraction element alsoincludes a feed of extraction gas, particularly an easily condensablegas, located downstream from the membrane, which lowers the partialpressure of the hydrogen downstream from the membrane by diluting theflow of permeated hydrogen. The result of this combination of technicalcharacteristics is that the permeation of the hydrogen is facilitated.

Preferably, in the case of this variant of embodiment of the invention,the extraction element with a permeable membrane is disposed in thefinal conversion reactor. The result of this combination of technicalcharacteristics is that the partial pressure of the hydrogen during thefinal conversion is lowered, which promotes the conversion of the carbonmonoxide into carbon dioxide.

Preferably, in the case of this variant of embodiment of the invention,the device also comprises means for regulating the temperature of thefinal conversion by acting on the flow rate and/or the input temperatureof the extraction gas.

Preferably, in the case of this variant of embodiment of the invention,the device is such that the permeable membrane is composed of aplurality of tubes that descend into the extraction element. Each tubeis shaped like a glove finger whose open end opens to the outside of theextraction element. The open end makes it possible to introduce theextraction gas into the tube.

Preferably, the device according to the invention is such that thepreheating means and the cooling heat exchanger are combined in arecovery exchanger so that the reagents and the conversion productscirculate continuously through the recovery exchanger.

Preferably, in the case where the device is more specifically intendedto produce hydrogen for the purpose of supplying a fuel cell runningwith air, the device according to the invention also comprises anelement for reducing the pressure of the conversion products and/or thefinal conversion products and/or the hydrogen produced, making itpossible to compress the air required to run the fuel cell.

Preferably, the device according to the invention can also be combinedwith a hydrogen production unit that generates a flow of oxygen,particularly by means of an electrolyzer. The result of this combinationof technical characteristics is that it is thus possible:

to limit the cost of producing the oxygen consumed in the methodaccording to the invention, and

to increase the overall quantity of hydrogen produced.

Preferably, the device according to the invention can also be combinedwith a nitrogen production unit that generates a flow of oxygen. Theresult of this combination of technical characteristics is that it isthus possible to limit the cost of producing the oxygen consumed in themethod according to the invention.

Other characteristics and advantages of the invention will becomeapparent through the reading of the description of variants ofembodiment of the invention given as an illustrative and non-limitingexample, and of

FIG. 1, which illustrates the variation in the fraction (fa) ofhydrocarbon oxidized with pure oxygen as a function of the reagentpreheating temperature in the case of diesel fuel,

FIG. 2, which illustrates the variation in the fraction (fa) ofhydrocarbon oxidized with air as a function of the reagent preheatingtemperature in the case of diesel fuel,

FIG. 3, which illustrates, in block diagram form, a variant ofembodiment of a unit for producing pure hydrogen stored under pressure,

FIG. 4, which illustrates, in block diagram form, another variant ofembodiment of a unit for producing pure hydrogen, intended to be usedimmediately in a low-temperature, low-pressure PEMFC-type fuel cell,

FIG. 5, which illustrates, in block diagram form, another variant ofembodiment of a unit for producing a mixture of hydrogen and carbondioxide, intended to be used immediately in a low-temperature,medium-pressure PEMFC-type fuel cell,

FIG. 6, which illustrates in block diagram form, another variant ofembodiment of a unit for producing a mixture of hydrogen and carbondioxide, intended to be used immediately in a high-temperature,medium-pressure SOFC-type fuel cell,

FIG. 7, which illustrates a variant of embodiment of a means forpreheating the reagents and a heat exchanger for cooling the associatedproducts, constituting a regeneration system, the regeneration systembeing combined with a conversion reactor,

FIG. 8, which illustrates another variant of embodiment of a means forpreheating the reagents and a heat exchanger for cooling the associatedproducts, constituting a recovery exchanger, the recovery exchangerbeing combined with a conversion reactor,

FIG. 9, which illustrates in a graph the increase in the efficiency ofthe hydrogen permeation as a function of the ratio between the molarflow rate of the extraction gas downstream from the membrane and themolar flow rate of the hydrogen to be extracted upstream from themembrane,

FIGS. 10 a and 10 b, which illustrate a reactor for converting CO intoCO₂ equipped with a hydrogen-permeable membrane, supplied withextraction water vapor on the downstream end

FIG. 11, which illustrates a reactor for converting CO into CO₂,equipped with a series of closed-end tubes that descend into the core ofthe reactor, each of which supports a hydrogen-permeable membrane.

We will now describe FIG. 1. This figure illustrates the variation inthe fraction (fa) of hydrocarbon oxidized with pure oxygen as a functionof the reagent preheating temperature in the case of diesel fuel. Asthis graph shows, and as the description below explains, the fraction(fa) of hydrocarbon oxidized depends on the desired conversiontemperature. The curves shown respectively correspond to the followingconversion temperatures (Tconv): 1000° C., 1200° C., 1400° C. They havebeen plotted for water factor (fe) values equal to 1.5 and a pressure of5 bar. In the sense of the present invention, the term water factor (fe)means the ratio between the flow of water actually made available byinjection into the conversion reactor and the stoichiometric flow ofwater required for a complete conversion of the fraction of hydrocarbonto be converted:C_(n)H_(m)O_(p) +fa(n+m/4−p/2)(O₂+λN₂+[fe(1−fa)(2n−p)−fa(m/2)]H₂O→nCO₂+(1−fa)(2n+m/2−p)H₂+faλ(n+m/4−p/2)N₂+(fe−1)(1−fa)(2n−p)H₂O

The water factor has an influence on the formation of soot, carbonparticles or polyaromatic hydrocarbons during the conversion. FIG. 1shows that fa diminishes when the preheating temperature of the reagentsincreases. In fact, the amount of energy supplied with preheatedreagents makes it possible to reduce the fraction of fuel to be burnedin order to reach the desired temperature level and to promote theendothermic conversion reactions.

Such figures can be established for each fuel or mixture of fuels andare not specific to diesel fuel. Nor are they specific to the reformingmethod used (vapor reforming or partial oxidation, catalytic ornon-catalytic, etc.).

Any conversion of a hydrocarbon into hydrogen using water vapor,possibly in the presence of oxygen, requires obtaining a sufficienttemperature level in the conversion reactor. The temperature level to beapplied depends both on the hydrocarbon to be converted and on whetheror not a catalyst is present. For example, in the case of a catalyticvapor reforming type reaction, a temperature of 200 to 250° C. issufficient in the case of methanol. If on the other hand the fuel ismethane, temperatures of 800 to 950° are necessary. The partialoxidation of gasoline can be conducted at 800° C. in the presence of acatalyst and at 1200° C. in the absence of a catalyst. Non-catalyticconversion using water vapor requires 1200° C. for any fuel and 1400° C.to obtain in less than one second a complete conversion, i.e., one thatreleases products that are free of even light hydrocarbons such asmethane, ethane or ethylene.

It order to reach these temperature levels at the end of conversion, itis wise to preheat the reagents. A portion of this preheating heat canbe recovered by cooling the products that leave the conversion reactor,and transferred to the reagents through external exchange. On the otherhand, it is technologically easier, and also faster, to supply heat togasses at a high temperature (higher than 800° C., for example) byoxidizing a fraction of the fuel, either with air, with oxygen, or withan oxygen-rich flow; the other, non-oxidized fraction of this fuel beingconverted into a mixture of hydrogen and carbon monoxide and dioxide.

For an adequate conversion temperature, a given water factor and achosen reagent preheating temperature, the fraction fa and the flow ofoxygen can be determined, as shown in FIG. 1. Thus, the three reagentflows to be placed in contact inside the conversion reactor areidentified.

The introduction into the conversion reactor of the preheated reagents,and in particular pure oxygen, generates highly active oxidation zonesin contact with the hydrocarbon, which can lead to very hightemperatures, for example higher than 2500° C. In the present invention,one must therefore be careful:

(i) first, to simultaneously introduce the hydrocarbon and the watervapor required for the conversion, so that the water vapor absorbs partof the energy given off by the oxidation of the hydrocarbon,

(ii) second, to organize the gradual injection of the reagents into thereactor and their mixture inside this reactor so as to gradually releasethe oxidation energy, as well as the energy required for the conversion,and thus establish a satisfactory temperature profile inside thereactor, and

(iii) and possibly, to provide thermal protection for the walls, forexample using a parietal film of hydrocarbons and/or water vapor that isrelatively cool compared to the reaction mixture.

The combination of these technical characteristics, and in particularthe proper use of a flow of nearly pure oxygen, makes it possible toobtain a nearly complete conversion of the hydrocarbon into hydrogen andCO/CO₂: light hydrocarbons such as methane, ethylene, and ethane, aswell as polyaromatic hydrocarbons, are present only in trace amounts.Thus, the products of the conversion contain only H₂, CO, CO₂ and H₂Oand are not diluted in nitrogen.

The hydrogen conversion reaction being endothermic, no matter how highthe preheating temperature, it will be necessary in all cases to oxidizea fraction of the hydrocarbon in order to compensate for the heat of theconversion reaction. This minimum fraction to be burned can bedetermined as a function of the fuel's enthalpy of formation and itscomposition. This particular value of fa is marked v. This value ischaracteristic of the fuel. It is equal to 0.2565 in the case of dieselfuel.

Knowing the value of fa and the value of v relative to the fuel makes itpossible to directly determine the value of the hydrogen productionyield, give or take a few losses, in the subsequent steps of the method.The yield η is equal to:η=(1−fa)/(1−v)

In the case of a non-catalytic conversion of diesel fuel with oxygen at1400° C., with a preheating of the reagents at 700° C., the yield isequal to:η=(1−0.374)/(1−0.2656)=0.852.

The flows of oxygen and diesel fuel to be used are therefore in a ratioof 1.27. A higher preheating temperature, with exchangers made ofceramic material, produces better yields. Yields of 80 to 90% aretherefore attainable with the technology according to the invention foroxygen and diesel fuel consumption in a ratio of 1.15 to 1.40 andhydrogen production yields of 0.283 to 0.253 kg H₂ per kg of dieselfuel.

If air were used instead of oxygen, the value of v would be unchanged,but higher values of fa would be required to reach the same conversiontemperatures. In fact, it is necessary to heat all of the nitrogen thatis injected into the conversion reactor at the same time as the oxygen.FIG. 2 illustrates, in the case of diesel fuel, the variation in thefraction (fa) of hydrocarbon oxidized with air as a function of thereagent preheating temperature. To facilitate the comparison of FIGS. 1and 2, the desired conversion temperatures are the same (1000, 1200 or1400° C.) as are the water factor fe=1.5 and the pressure P=5 bar.

Thus, for diesel fuel, for a conversion temperature equal to 1400° C.and a preheating at 700° C., a value of fa equal to 0.444 is necessary.From this, it may be deduced that the conversion yield with air is:η=(1−fa)/(1−v); or η=(1−0.444)/(1−0.2656)=0.757

This yield is clearly more advantageous than with pure oxygen (0.852).

Moreover, with air, the oxidation of the fraction of the fuel and theconversion of the remaining fraction are less sudden than with oxygen.The maximum temperatures reached are lower, and there may remain largercontents of light hydrocarbons such as methane, ethylene and ethane aswell as polyaromatic hydrocarbons. These contents are on the order of afew per thousand to a few percent, depending on the family of conversionmethods used and the temperature applied.

We will now demonstrate that the use of pure or nearly pure oxygen makesit possible to operate under pressure, which has several advantages. Wewill also demonstrate that it is possible to use pure or nearly pureoxygen under pressure without thereby reducing the yield.

Reforming units on petrochemical sites commonly operate at highpressures of several tens of bar. On the other hand, for a small-scaleunit that feeds, for example, a low-pressure fuel cell, using a partialoxidation or autothermal vapor reforming unit at high pressure isdetrimental to the overall efficiency of the system since it isnecessary to compress the air to be injected into the conversionreactor, which is energy-expensive. It is therefore preferable tooperate at a pressure close to the atmospheric pressure.

Conversely, in the case of the present invention, with a supply ofoxygen rather than air, the cost of compressing the oxidant becomesnegligible: either the oxygen is supplied in gaseous form in bottles orreservoirs already compressed to 200 bar or more, or the oxygen issupplied in liquid form under a few bar of pressure, but the compressionenergy of the liquid is negligible. It is therefore possible andadvantageous to perform the hydrogen production steps between 30 and 60bar; this technical characteristic provides several advantages:

(i) The high pressures of the gasses lead to higher gas densities,higher heat exchange coefficients through the walls, and often alsofaster chemical kinetics, making it possible to considerably reduce thesize of the equipment of the method.

(ii) The high pressure of the products makes it possible to use ahydrogen-permeable membrane, a membrane that normally requires typicalpartial pressure difference of 15 bar (in reality from a few bar to 40or 50 bar), in order to efficiently extract hydrogen and separate CO₂and H₂, as explained below.

(iii) The high pressure of the products makes it possible, aftercooling, to easily condense the water contained in the products and torecycle it for use in the conversion reactor.

(iv) The high pressure of the products makes it possible in certaincases, as explained below, to condense the carbon dioxide.

(v) With a method of production between 30 and 60 bar, the pressure ofthe products can also be skillfully used, as explained below, to reducethe use of energy-expensive auxiliary equipment and thus increase theoverall efficiency of the installation.

A hydrogen production unit according to the invention can be embodied invarious ways. Four variants of embodiment are shown as examples in FIGS.3 through 6.

We will now describe FIG. 3, which illustrates, in block diagram form, avariant of embodiment of a unit for producing pure hydrogen stored underpressure.

The production unit, also called the device 1, is composed of thefollowing elements:

-   -   a hydrocarbon reservoir: 2    -   a reservoir for oxygen under pressure or in liquid form: 3    -   a CO+H₂ conversion reactor at 60 bar: 4    -   a means for preheating the reagents: 5    -   a first heat exchanger for cooling the products: 6 a    -   a reactor for the final conversion of CO into CO₂: 11    -   a hydrogen-permeable membrane at 60 bar/20 bar: 7    -   a hydrogen compression element: 8    -   an H₂ storage reservoir: 10    -   a carbon dioxide condenser at 60 bar: 14    -   a water condenser at 60 bar: 13    -   a second cooling exchanger at 60 bar: 6 b    -   a post-combustion of the final products at 60 bar: 12    -   a storage container for the CO₂ at 60 bar: 16    -   a water reservoir at 60 bar: 15

The production unit 1 is used to produce pure hydrogen. The latter isstored under high pressure (200 to 350 bar or more) for later use. Thepressure in the conversion reactors 4 of this unit is on the order of 50to 60 bar. Downstream from the membrane 7, the pressure of the flow ofhydrogen extracted is still significant (20 to 30 bar); the compressioneffort required to reach the storage pressure is thus considerablyreduced.

We will now describe FIG. 4, which illustrates, in block diagram form,another variant of embodiment of a unit for producing pure hydrogen,intended to be used immediately in a low-temperature, low-pressurePEMFC-type fuel cell.

The production unit, also called the device 1, is composed of thefollowing elements:

-   -   a hydrocarbon reservoir: 2    -   a reservoir for oxygen under pressure or in liquid form: 3    -   a CO+H₂ conversion reactor at 60 bar: 4    -   a means for preheating the reagents: 5    -   a heat exchanger for cooling the products: 6    -   a reactor for the final conversion of CO into CO₂: 11    -   a hydrogen-permeable membrane at 60 bar/20 bar: 7    -   a carbon dioxide condenser at 60 bar: 14    -   a water condenser at 60 bar: 13    -   a cooling exchanger at 60 bar: 6    -   a post-combustion of the final products at 60 bar: 12    -   a storage container for the CO₂ at 60 bar: 16    -   a water reservoir at 60 bar: 15    -   an air compression element at 1 bar/2 bar: 19    -   an element for reducing the pressure of the hydrogen from 20        bar/2 bar: 18    -   a PEFC fuel cell at 2 bar and 80° C.: 17

The production unit 1 produces pure hydrogen, which is immediately putto use in another system, for example a PEMFC (Proton Exchange MembraneFuel Cell) type fuel cell 17, running at a relatively low temperature(60 to 120° C.) and low pressure (between 1 and 5 bar). The productionunit is identical to the one in FIG. 3 until just downstream from themembrane 7, where the pressure of the flow of hydrogen extracted isstill significant (20 to 30 bar) and its temperature is high (350° C.).The release of pressure from the hydrogen downstream from the membrane 7by means of a turbo compressor 18, 19 supplies the energy forcompressing the air that feeds the cell 17, which normally requires apiece of auxiliary equipment that is costly in terms of the overallefficiency of the method.

We will now describe FIG. 5, which represents, in block diagram form,another variant of embodiment of a unit for producing a mixture ofhydrogen and carbon dioxide, intended to be used immediately in alow-temperature, medium-pressure PEMFC-type fuel cell. The productionunit, also called the device 2, is composed of the following elements:

-   -   a hydrocarbon reservoir: 2    -   a reservoir for oxygen under pressure or in liquid form: 3    -   a CO+H₂ conversion reactor at 60 bar: 4    -   a means for preheating the reagents: 5    -   a first heat exchanger for cooling the products: 6 a    -   a reactor for the final conversion of CO into CO₂: 11    -   a water condenser at 7 bar: 13    -   a second heat exchanger for cooling the products: 6 b    -   a post-combustion of the final products at 7 bar: 12    -   a water reservoir at 7 bar: 16    -   an air compression element at 1 bar/7 bar: 19    -   an element for reducing the pressure of H₂/CO₂ from 60 bar/7        bar: 18    -   a CO₂ storage container at 7 bar: 15

The production unit 1 produces hydrogen for immediate use in a mixturewith CO₂ in a fuel cell 17 at a relatively low temperature and mediumpressure. In the case of this variant of embodiment, the production unit1 does not include a hydrogen permeation membrane 7, but includes anadditional cooling 6 b of the products during the final conversion ofthe CO into CO₂. The hydrogen production unit 1 operates at a high levelof pressure (30 to 60 bar). The energy recovered during the release ofpressure 18, 19 from the H₂/CO₂ mixture makes it possible to compressthe air admitted into the fuel cell 17. The recoverable energy issubstantial since the mass and volume rate of the H₂+CO₂ mixture whosepressure is to be reduced is higher than in the case of the productionunit represented in FIG. 4. It is possible to have the cell 17 run at ahigher pressure (5 or 7 absolute bar rather than 1 bar), which promotesthe recycling of the water leaving the cell 17 in order to feed theconversion reactor 4, and which also promotes the compactness of theequipment.

We will now describe FIG. 6, which illustrates, in block diagram form,another variant of embodiment of a unit for producing a mixture ofhydrogen and carbon dioxide, intended to be used immediately in ahigh-temperature, medium-pressure SOFC-type fuel cell.

The production unit, also called the device 1, is composed of thefollowing elements:

-   -   a hydrocarbon reservoir: 2    -   a reservoir for oxygen under pressure or in liquid form: 3    -   a CO+H₂ conversion reactor at 60 bar: 4    -   a means for preheating the reagents: 5    -   a first heat exchanger for cooling the products: 6 a    -   a water condenser at 7 bar: 13    -   a second cooling exchanger at 7 bar: 6 b    -   a post-combustion of the final products, CO/H₂ at 7 bar: 12    -   a water reservoir at 7 bar: 15    -   an air compression element at 1 bar/7 bar: 19    -   an element for reducing the pressure of H₂/CO₂ from 60 bar/7        bar: 18    -   an SOFC fuel cell at 7 bar and 800° C.: 20    -   a CO₂ storage container at 7 bar: 16

The production unit 1 produces hydrogen in a mixture with CO and CO₂ foruse in an SOFC (Solid Oxide Fuel Cell) type fuel cell running at a hightemperature (600 to 900° C.) and relatively medium pressure (between 1and 7 bar). In the case of this other variant of embodiment, theproduction unit 1 does not include a hydrogen-permeable membrane 8either; nor does it include the final conversion 11 of the CO into CO₂since the CO can be used by the SOFC. The hydrogen production unit 1operates at a high level of pressure (30 to 60 bar). The energyrecovered during the release of pressure 18 from the H₂/CO/CO₂ mixturemakes it possible to compress the air 19 admitted into the fuel cell 17.It is possible to have the SOFC run at a medium pressure (5 or 7absolute bar instead of 1), which promotes the recycling of the waterleaving the cell in order to feed the conversion reactor 4, as well asthe compactness of the equipment.

The means for preheating the reagents 5 and the heat exchanger forcooling 6 the products in the case of the variants of embodimentillustrated in FIGS. 3 through 6 may advantageously be combined so thatthe energy recovered from the products is transferred to the reagents.Both capabilities of the combination, regeneration or recovery, can beimplemented in the variants of embodiment described above.

We will now describe FIG. 7, which illustrates a variant of embodimentof a means for preheating the reagents 5 and a heat exchanger forcooling the associated products 6, constituting a regenerative system.In the case of the variant of embodiment represented in FIG. 7, thereagent preheating means previously referenced 5 is referenced 22, andthe cooling heat exchanger previously referenced 6 is referenced 23.

In the case of regenerative exchangers, the heat is stored in theelements made of ceramic material placed in the reagent preheating means22 and in the cooling heat exchanger 23. The reagent preheating means 22and the cooling heat exchanger 23 are disposed on either side of theconversion reactor 4.

The flows are periodically alternated. The cold reagents enter thereagent preheating means 22, wherein the ceramic elements are hot, heatup on contact with it and cool it, while the hot products enter thecooling heat exchanger 23, which is relatively cold, cool off in contactwith the ceramic elements and reheat them. After a certain amount oftime (on the order of one minute to 30 minutes depending on the size ofthe installation), the flows are reversed by means of valves 21, and theroles of the reagent preheating means 22 and the cooling heat exchanger23 are reversed. The reagents flow into the cooling heat exchanger 23,which has become hot enough to serve as the reagent preheating means 22,then pass through the conversion reactor 4 in the opposite direction.The conversion products leave the conversion reactor 4 in the directionof the reagent preheating means 22. The latter has become cold enough toserve as the cooling heat exchanger.

The ceramic elements have the advantage of being able to be used at avery high temperature.

We will now describe FIG. 8, which represents a variant of embodiment ofa means for preheating the reagents 5 and a heat exchanger for coolingthe associated products 6, constituting a recovery system 24.

In the case of the variant of embodiment represented in FIG. 8, themeans for preheating the reagents 5 and the heat exchanger for coolingthe products 6 form two sides of the same piece of equipment, and theheat is transferred from one to the other through the impermeablesurface that separates them. This configuration has the advantage ofcontinuous operation and does not require a system of flow-reversing andcontrol valves. The thermal inertia is also much lower.

The hydrocarbons, the oxygen and the water or vapor enter the recoverysystem 24, where they are heated, cooling the hot products of theconversion. They are then injected into the conversion reactor 4 on theopposite side of the recovery system 24 through feed circuits 25. Thehot conversion products then enter the recovery system 24.

In the case of the four variants of embodiment represented in referenceto FIGS. 3 through 6, after the extraction of the hydrogen or its use bythe fuel cell, the gas may still contain a small amount of residualhydrogen. The same is true of the CO after its conversion into CO₂ orits use by the SOFC-type fuel cell. The gas is then subjected to apost-combustion 12 of these residues, which transforms them into H₂O andCO₂.

The gas, under high pressure (50 or 60 bar in the case of the variantsof embodiment in FIGS. 3 and 4) or medium pressure (5 to 7 bar in thecase of the variants of embodiment in FIGS. 5 and 6), no longer containsanything other than water vapor and carbon dioxide (with small traces ofCO, H₂ if the post-combustion is incomplete, and nitrogen if the oxygenused is not pure). Cooling it to a temperature on the order of 40° C.will result in the condensation 13 of nearly all of the water, which canbe recycled back to the beginning of the hydrocarbon conversion processvia a reservoir of water under pressure 15.

The residual gas is then nothing but nearly pure CO₂ (with traces of CO,H₂, N₂, H₂O). At a pressure of 60 bar, the CO₂ can be easily condensedby cooling in contact with a wall at ambient temperature. The effectiverate of condensation of the CO₂ will depend on the temperature of thecold wall and the level of residual impurities in the gas: for example,at 60 bar and with a wall at 110° C., a 92% to 99.2% condensation of theCO₂ will be obtained if the traces of CO, H₂ and N₂ represent 2% to0.2%, respectively, in the products leaving the post-combustion chamber.The CO₂ can then be stored in dense liquid form. Pressures as low as 30bar are acceptable for condensing the CO₂; in that case, it is necessaryto use a refrigerant at negative temperatures such as −20° C. in orderto obtain substantial levels of CO₂ condensation, commensurate with thelevel of residual impurities in the gas.

In the case of the variants represented in FIGS. 5 and 6, the flow ofCO₂ generated can be stored at a pressure of 7 bar, or possiblyrecompressed in order to be condensed.

In all cases, it is possible not to discharge the CO₂ generated by thehydrocarbon conversion into the atmosphere. It may be re-used in aCO₂-consuming process or stored in underground layers. Finally, if thehydrogen is from a fossil hydrocarbon source, its production will nothave generated any additional greenhouse effect. If the hydrogen is froma renewable biomass source, its production is accompanied by a carbonsink.

FIGS. 3 and 4 show two variants of embodiment comprising two successivesteps. The purpose of one step is to convert CO in to CO₂ using thegas's catalytic reaction to water: CO+H₂O→CO₂+H₂. The purpose of theother step is to extract the hydrogen formed by means of a membrane 7.The use of oxygen in place of air promotes the extraction by themembrane 7 since the partial pressure of the hydrogen, which is notdiluted in nitrogen, is higher.

Moreover, it is advantageous to be able to combine several functions inthe same piece of equipment. The use of a vector gas or an easilycondensable extraction gas, for example water vapor or ammonia,downstream from the permeation membrane 7, makes it possible to lowerthe partial pressure of the hydrogen downstream and thus to extract moreof the hydrogen in the reformate. FIG. 9 shows the increase in theefficiency of the hydrogen extraction as a function of the ratio betweenthe molar flow rate of the hydrogen to be extracted and the molar flowrate of the flow of extraction gas. In the case illustrated in FIG. 9,the total pressure upstream from the membrane 7 is 45 bar, the molarfraction of the hydrogen upstream is 50.9%, and the total pressuredownstream from the membrane 7 is 5 bar. Extraction efficiencies of 90to 100% may be obtained, even with back pressures of 5 bar downstreamfrom the membrane 7. After the extraction of the hydrogen, the flow ofextraction gas may be condensed by cooling so as to be recycled to theextraction membrane, leaving behind a flow of pure hydrogen to be usedor stored.

Any gas that is inert with respect to hydrogen and the membrane, such asnitrogen, argon, water vapor, ammonia, etc., may be used to lower thepartial pressure of the hydrogen downstream from the membrane and thusextract the hydrogen more easily. However, it is advantageous to use aneasily condensable extraction gas such as water vapor or ammonia; a stepfor cooling and condensing the vector gas/hydrogen mixture will make itpossible to separate them and to recover pure hydrogen.

We will now describe, in reference to FIGS. 10 a and 10 b, two variantsof embodiment according to the invention of a reactor for the finalconversion of CO into CO₂ 11, comprising a hydrogen-permeable membrane 7that makes it possible to extract the hydrogen. In the case oflow-capacity, small scale installations, it is possible to organize thepermeation chamber 27 so that it is concentric to the conversionreactor. In the case of the variant of embodiment represented in FIG. 10a, the hydrogen is extracted at the center of the final conversionreactor 11.

The membrane tube 26 is placed on the axis of the chamber 27 and is fedwith extraction water vapor. The conversion catalyst is placed in thering-shaped chamber around the membrane tube 26 and is passed through bythe gasses to be converted, generally in the opposite direction from theextraction water vapor. In the case of the variant of embodimentrepresented in FIG. 10 b, the hydrogen is extracted at the periphery ofthe final conversion reactor 11. The water vapor for extracting thehydrogen circulates at the periphery of the final conversion reactor 11.The conversion catalyst is placed in the center.

We will now describe, in reference to FIG. 11, another variant ofembodiment according to the invention of a reactor for the finalconversion of CO into CO₂ 11, equipped with a series of closed-end tubesthat descend into the core of the reactor, each of which supports ahydrogen-permeable membrane that makes it possible to extract hydrogen.

In the case of a high-capacity installation, the membrane surface to beinstalled would result in an excessive diameter and length if theconfiguration represented in FIG. 10 a or 10 b were retained. Likewise,the quantity of catalyst required would result in a ring that is toothick. For this reason, the compositions and temperatures in eachsection would not be homogeneous. It is preferable to divide up thecatalyst thickness using a number of membrane tubes 26 shaped like thefingers of a glove. The tubes 26, of small diameter and length, descendfrom the external wall right into the core of the conversion reactor 11.

Reactors like those described in reference to FIGS. 10 a and 10 b makeit possible not to separate the steps for the final CO/CO₂ conversionand for the extraction of the hydrogen. They are performed in the samechamber. It is thus possible to reduce the partial pressure of thehydrogen during the final CO/CO₂ conversion and thereby shift theequilibrium toward the formation of CO₂ and H₂O; the conversion reactionis accelerated. A smaller quantity of catalyst or a smaller size chambermay be used to achieve equivalent performance. This configuration ispossible because the conversion of the CO into CO₂ and the extractionthrough a hydrogen-permeable membrane are done at the same temperaturelevel: on the order of 250 to 400° C. The reaction of the gas to wateris exothermic, and heat must be extracted in order to maintain the gaswithin the optimal operating temperature range of the catalyst. In thecase where the membrane is located inside the final conversion reactor,the flow of extraction water vapor can advantageously be used to coolthe CO/CO₂ conversion chamber. Likewise, when the installation is coldand must be reheated in order for the catalyst and the permeablemembrane to reach their best operating temperature range, the flow ofextraction water vapor may be used to supply heat to this conversionreactor. The tube or tubes that support the permeation membrane 26 andare passed through by the extraction water vapor can advantageouslyserve as heat exchangers, thus avoiding the use of specific equipmentfor this heat exchange function. The temperature of the conversionchamber can thus be regulated by varying the flow rate and thetemperature of the flow of extraction water vapor.

Nitrogen may be produced by distilling air under cryogenic conditions.The production of one kg of nitrogen is accompanied by the production of0.30 kg of oxygen. This oxygen, in liquid form, may be used onsite toproduce hydrogen using the method according to the invention describedin reference to FIGS. 3 through 6. It may also be transported in orderto be used at another site using the method according to the inventiondescribed in reference to FIGS. 3 through 6.

With the oxygen produced, for an 80 to 90% energy efficiency of themethod for producing hydrogen, the consumption of diesel fuel isrespectively equal to 0.21 kg/kg of nitrogen and 0.26 kg/kg of nitrogenfor a quantity of captured CO₂ respectively equal to 0.67 kg per kg ofnitrogen and 0.82 kg per kg of nitrogen. The quantity of hydrogengenerated is respectively equal to 0.054 kg of H₂ per kg of nitrogenproduced and 0.073 kg of H₂ per kg of nitrogen produced, representing achemical energy of 7.7 to 10 MJ and an electrical energy of 1.1 to 1.45kWh after use in a fuel cell.

Hydrogen can also be produced by water electrolysis. The production ofone kg of electrolytic hydrogen is accompanied by the production of 8 kgof oxygen. The electrolyzers operate under medium pressure, from a fewbar to several tens of bar. The oxygen produced may be put to useaccording to any of the variants of embodiment represented in FIGS. 3through 6. The variant of embodiment represented in FIG. 3, however, hasthe advantage of using the oxygen onsite to produce hydrogen. The methodaccording to the invention makes it possible to obtain a flow ofchemical hydrogen in addition to the electrolytic hydrogen, whilecontributing to CO₂ capture and to the amortization of all the utilitiesfor conditioning the hydrogen produced.

The leverage is considerable, since with 8 kg of oxygen produced, for an80 to 90% energy efficiency of the chemical method for producinghydrogen, the consumption of diesel fuel is respectively equal to 5.75to 6.9 kg/kg of electrolytic hydrogen for a quantity of captured CO₂respectively equal to 19.1 kg per kg of electrolytic hydrogen and 21.8kg per kg of electrolytic hydrogen. The quantity of hydrogen generatedis respectively equal to 1.45 kg of chemical hydrogen per kg ofelectrolytic hydrogen and 1.96 kg of chemical hydrogen per kg ofelectrolytic hydrogen.

Combining the two methods results in an increase in the quantity ofhydrogen produced by a factor of nearly 3, which largely compensates forthe efficiency loss of electrolysis.

1-21. (canceled)
 22. A method for producing hydrogen from a hydrocarbon with high energy efficiency while releasing very low or zero levels of carbon dioxide and pollutants, said method comprising the steps of: preheating reagents comprising hydrocarbons, a nearly pure flow of oxygen and water to be vaporized; oxidizing a portion of said hydrocarbons using the flow of nearly pure oxygen and converting nearly all of the remaining portion of said hydrocarbons into hydrogen, carbon monoxide and carbon dioxide by supplying heat and water vapor at suitable temperature, thereby improving the hydrogen production yield and forming a conversion product comprising a mixture of said hydrogen, said carbon monoxide, said carbon dioxide, and excess water vapor; cooling said conversion product to recover a fraction of the thermal energy of said conversion product which can be used to preheat said reagents and condensing at least part of the water vapor contained in said conversion product; extracting said hydrogen from said conversion product for consumption or storage for later consumption; and wherein said steps of said method being performed at suitably high pressures above 30 bar to intensify the heat exchanges, promote the liquefaction of said carbon dioxide and the condensation of the water vapor by cooling, and/or improve the overall efficiency of said method.
 23. The method of claim 22, further comprising the step of converting said carbon monoxide in said conversion product into said carbon dioxide to form a final conversion product containing only carbon dioxide and uncondensed water vapor.
 24. The method of claim 23, further comprising the steps of condensing said carbon dioxide and capturing said carbon dioxide in a liquid form.
 25. The method of claim 23, wherein the step of extracting hydrogen extracts hydrogen from said conversion product using a membrane that is selectively permeable to hydrogen; and further comprising the step of lowering the partial pressure of said hydrogen downstream from said permeable membrane by diluting the flow of permeated hydrogen in a flow of extraction gas, thereby facilitating the permeation of the hydrogen and recovery of pure hydrogen through condensation of said extraction gas.
 26. The method of claim 25, wherein the step of extracting is performed simultaneously with the step of converting to lower the partial pressure of said hydrogen during said step of converting, thereby promoting the conversion of said carbon monoxide into said carbon dioxide.
 27. The method of claim 26, wherein the step of converting further comprises the step of regulating the temperature by adjusting the flow rate and/or the temperature of said extraction gas.
 28. The method of claim 22, wherein said steps of preheating and cooling are performed in a recovery exchanger so that said reagents and said conversion product circulate continuously through said recovery exchanger.
 29. The method of claim 22, wherein said hydrogen extracted from said conversion product feeds a fuel cell running with air; and further comprising the step of reducing the pressure of said conversion product and/or said hydrogen being fed to said fuel cell.
 30. The method of claim 22, further comprising the step of using a hydrogen production method to generate a flow of said nearly pure oxygen by electrolysis, thereby reducing the cost of producing said nearly pure oxygen consumed in said method and increasing the overall production of said hydrogen.
 31. The method of claim 22, further comprising the step of using a nitrogen production method to generate a flow of said nearly pure oxygen, thereby reducing the cost of producing said nearly pure oxygen consumed in said method.
 32. Apparatus for producing hydrogen from a hydrocarbon with high energy efficiency while releasing very low to zero levels of carbon dioxide and pollutants, said apparatus comprising: a reactor for converting hydrocarbons using water vapor at suitable temperature, said conversion reactor being supplied with nearly pure oxygen to oxidize a portion of said hydrocarbons and supplying heat to convert nearly all of the remaining portion of said hydrocarbons into hydrogen, carbon monoxide and carbon dioxide, thereby forming a conversion product comprising a mixture of said hydrogen, said carbon monoxide, said carbon dioxide and excess water vapor; a heating device for preheating reagents comprising said hydrocarbons, said nearly pure flow of oxygen, and water to be vaporized; at least one cooling heat exchanger for cooling said conversion product, for recycling a fraction of the thermal energy of said conversion product to preheat said reagents, and for condensing at least a part of the water vapor contained in said conversion product; and a hydrogen recovery unit comprising an extraction element for extracting said hydrogen from said conversion product for consumption in a hydrogen-consuming device, or storage in a hydrogen reservoir for later consumption; and wherein said first conversion reactor, said heating device, said heat exchanger, and said recovery unit operating at suitably high pressures above 30 bar to intensify the heat exchanges, increase the compactness of the method, promote the liquefaction of the carbon dioxide by cooling, promote the condensation of the water vapor by cooling, and/or improve the overall efficiency of the apparatus.
 33. The apparatus of claim 32, further comprising at least one final conversion reactor operating with said hydrogen recovery unit for converting said carbon monoxide in said conversion product into carbon dioxide to form a final conversion product containing only carbon dioxide and uncondensed water vapor.
 34. The apparatus of claim 33 further comprising a condenser for condensing said carbon dioxide and a container for storing said carbon dioxide in liquid form.
 35. The apparatus of claim 33, wherein said extraction element comprises a membrane that is selectively permeable to hydrogen for extracting hydrogen from said conversion product, wherein said extraction element is operable to receive a feed of extraction gas downstream from said permeable membrane, to lower the partial pressure of the hydrogen downstream from said permeable membrane and to dilute the flow of permeated hydrogen, thereby facilitating the permeation of the hydrogen and recovery of pure hydrogen through condensation of the extraction gas.
 36. The apparatus of claim 33, wherein said extraction element comprises a permeable membrane disposed inside said final conversion reactor, for lowering the partial pressure of the hydrogen during the conversion in said final conversion reactor, thereby promoting the conversion of the carbon monoxide into carbon dioxide.
 37. The apparatus of claim 36, wherein said final conversion reactor comprises a regulating device for regulating the temperature in said final reactor by acting on the flow rate and/or the input temperature of the extraction gas.
 38. The apparatus of claim 35, wherein said selectively permeable membrane is comprised of a plurality of tubes that descend into said extraction element, wherein each tube has the shape of a glove finger comprising an open end which opens to the outside of said extraction element to introduce said extraction gas into said tube.
 39. The apparatus of claim 32, wherein said heating device and said cooling heat exchanger are combined in a recovery exchanger so that said reagents and said conversion product circulate continuously through said recovery exchanger.
 40. The apparatus of claim 32, wherein said hydrogen extracted from said conversion product feeds a fuel cell running with air, and further comprising an element for lowering the pressure of said conversion product and/or said hydrogen produced to compress the air required to run said fuel cell.
 41. The apparatus of claim 32, further comprising a hydrogen production unit for generating a flow of oxygen through an electrolyzer.
 42. The apparatus of claim 32, further comprising a nitrogen production unit for generating a flow of oxygen to limit the cost of producing the oxygen consumed in said apparatus. 